I do 2-3/week but rotate with herring, Pacific saury, smoked trout or eel, etc.
If the metal toxicity were a problem I assume we'd see more real world diagnoses so I don't sweat it myself. Prenatal deficiencies are much more common so I'd err on the side of "eat everything". A lot of nonindustrial cultures hunted down seafood specifically for pregnant women.
Lots of: urban hiking, cycling, sprinting
Lots of: fresh meat, seafood, eggs, organs, tubers, starchy fruits, low-energy plants, meat fat, dairy fat, oily fruits
Some: cured meat, dairy protein, sweet fruits, rice, peas, tree nuts, oily seeds
Minimal: soy, refined proteins, sugar, liquid carbohydrate, grains, beans, refined oils, peanuts